The basic processes for obtaining useful color images from exposed color photographic silver halide materials include several steps of photochemical processing such as color development, silver bleaching, silver halide fixing and water washing or dye image stabilizing using appropriate photochemical compositions.
Photographic color developing compositions are used to process color photographic materials such as color photographic films and papers to provide the desired dye images early in the photoprocessing method. Such compositions generally contain color developing agents, for example 4-amino-3-methyl-N-(2-methane sulfonamidoethyl)aniline, as reducing agents to react with suitable color forming couplers to form the desired dyes. U.S. Pat. No. 4,892,804 (Vincent et al) describes conventional color developing compositions that have found considerable commercial success in the photographic industry. Other known color developing compositions are described in U.S. Pat. No. 4,876,174 (Ishikawa et al), U.S. Pat. No. 5,354,646 (Kobayashi et al) and U.S. Pat. No. 5,660,974 (Marrese et al).
It is common practice to add a "replenishing" solution to the color developing composition in the processing machine in order to replace photochemicals that are depleted during reaction or carried away by the processed materials. Such replenishment insures uniform development and maximum stability of the color developing agent.
Color developing compositions are commonly supplied in three or more "parts" (or solutions) that are mixed immediately before use. Multiple parts are often required in order to separate and preserve the chemical activity and solubility of components that may otherwise deteriorate or react with each other when they are stored together for long periods of time under alkaline conditions. For example, one part might include a color developing agent. Another part might contain agents to preserve the alkalinity of the mixed color developing composition. Still another part may include an optical brightener. Upon combination of all parts and additional water, a color developing composition can usually be obtained for use in the photographic processing machine.
It is generally known that the concentrations of various photochemicals and pH (typically alkaline) used in a photographic processing bath must lie within certain narrow limits in order to provide optimal performance. A relatively small change in any of the component concentrations or pH can diminish desired photochemical activity, storage stability, solution homogeneity, or any combination of these. Thus, each "part" or solution used to make a working strength solution must be formulated to provide a desired balance of all desired properties.
While multi-part color developing compositions are widely used in the photoprocessing industry (including in what are known as "minilabs"), they are sometimes supplied in containers that are not completely emptied during use. The residual solutions must therefore be discarded into the environment. In some countries, any of these solutions having extremely low or high pH are considered hazardous wastes and require more costly and tedious disposal procedures.
In addition, multi-part color developing compositions may also be corrosive to low carbon steel that may be present in photoprocessing equipment. This corrosivity may also be a result of extremely high or low pH.
To the unskilled person in the art, a simple solution to the problems would be to adjust pH so the solutions are no longer considered hazardous or corrosive. However, as pointed out above, this is not a simple matter and requires expert and complicated balancing of various components and pH to maintain stability and photochemical activity. As the number of "parts" and components in each increase, the number of possible modifications increases correspondingly, making it even harder to find the truly viable (that is commercial) options that will solve all of the problems simultaneously.